Active probe for an atomic force microscope and method of use thereof

Abstract

An AFM that combines an AFM Z position actuator and a self-actuated Z position cantilever (both operable in cyclical mode and contact mode), with appropriate nested feedback control circuitry to achieve high-speed imaging and accurate Z position measurements. A preferred embodiment of an AFM for analyzing a surface of a sample in either ambient air or fluid includes a self-actuated cantilever having a Z-positioning element integrated therewith and an oscillator that oscillates the self-actuated cantilever at a frequency generally equal to a resonant frequency of the self-actuated cantilever and at an oscillation amplitude generally equal to a setpoint value. The AFM includes a first feedback circuit nested within a second feedback circuit, wherein the first feedback circuit generates a cantilever control signal in response to vertical displacement of the self-actuated cantilever during a scanning operation, and the second feedback circuit is responsive to the cantilever control signal to generate a position control signal. A Z position actuator is also included within the second feedback circuit and is responsive to the position control signal to position the sample. In operation, preferably, the cantilever control signal alone is indicative of the topography of the sample surface. In a further embodiment, the first feedback circuit includes an active damping circuit for modifying the quality factor (“Q”) of the cantilever resonance to optimize the bandwidth of the cantilever response.